An Advanced and Detailed In Vitro Validation Procedure for the Radiolabeling of Carrier-Free Terbutaline Sulphate Dry Powder

Abstract

The aerodynamic properties of ^99mTc radiolabeled carrier-free terbutaline sulphate (TBS) have been thoroughly investigated following delivery by Turbuhaler^® (AstraZeneca Lund, Sweden). A full and detailed radiolabeling procedure is also reported. The in vitro radiolabel validation was performed to determine whether TBS radiolabeled in this way would be representative of the commercially available product Bricanyl^® Turbuhaler during clinical trials. The results indicated that variations in aerodynamic properties had been introduced and that the radiolabel would slightly underestimate the fine particle fraction of Bricanyl, but would nonetheless act as a suitable marker in vivo. Assumptions regarding the aerodynamic properties of doses likely to be received by clinical trial subjects were also examined. This has been achieved by extending the validation procedures beyond those usually reported to include dose number, time, and homogeneity dependent studies. It was found that doses extracted for testing purposes and simulated patient doses extracted shortly afterward had similar properties. Doses extracted 2 h after initial testing also had similar properties to the test doses. These results suggested that data from the test doses could be used for quality control purposes, would be representative of the doses to be received by clinical trial subjects, and that a short delay between initial testing and trial subject inhalation would be acceptable.